The present invention relates to a nuclear power reactor having an active zone containing a plurality of fuel elements containing a large number of rod-shaped fuel rods. The fuel elements are mounted between a lower and an upper grid plate. More particularly, the invention relates to a resilient tension device which is provided for each fuel element to tension hold the same between the grid plates.
The fuel elements are normally tightly packed and are subjected to a longitudinal flow of a fluid coolant which may be liquid or gaseous. Because of this flow, the fuel elements and the fuel rods contained therein can now be mechanically stressed in such a manner that vibrations can develop. Upon first impression, it would seem that this could be prevented by firmly clamping the fuel elements between the upper and lower grid plates which constitute part of the core frame. This, however, is not possible because of the different thermal expansion coefficients of the different materials used in the construction of the core. For this reason, the attempt has already been made to hold the fuel elements down against the flow pressure of the coolant by springs in the head portion and to thereby compensate for the differences in thermal expansion. However, this results in relatively complicated configurations because the vibrations of the fuel elements must be reliably avoided.